Experimental Study on Properties of Magnesium Phosphate Cement–Based Self-Compacting Concrete with High-Early Strength

Recently, magnesium phosphate cement (MPC) has received extensive research attention due to its fast construction, excellent bonding performance, and eco-friendly environment. Thus, some scholars believe that MPC is a promising candidate for the partial replacement of ordinary portland cement in construction engineering. However, most of the existing studies and applications of MPC mainly focused on the properties of cement materials and small construction applications, such as rapid repair and strengthening engineering, while the properties of MPC-based concrete were seldom reported. Moreover, there are still some problems that need to be solved, such as high raw material cost, short setting time, and concrete casting. In general, this greatly limits the mass construction application of MPC. This study discussed a new type of MPC-based self-compacting concrete with high early strength using mineral admixtures and composite retarders. Twenty-one mix proportions of MPC-based concrete were mixed with investigating the effect of aggregate cement ratios ($A/c$), mass ratios of fine aggregate to coarse aggregate ($m_s:m_g$), MgO purity and fineness, the water-cement ratio ($w/c$), and glacial acetic acid (GAC) content and mineral admixtures content on the fluidity, setting time, reaction temperature, and cubic compressive strength (CCS) at different curing ages (1, 3, 7, and 28 days), including a total of 252 concrete specimens, and the optimum mix proportion was also given. Finally, the CCS and setting time of the specimens were compared with those of the open literature, and a 4-m long full-scale beam was cast to verify the feasibility of MPC-based concrete in the actual mass pouring. The results indicated that the mix proportion with an MgO purity of 98 and average particle size of $125\mathrm{\mu m}$ had the highest late strength, higher early strength, longer setting time, and better self-compacting and workability under $A/c=1.3$, $m_s:m_g=1:5$, and $w/c=0.12$, and a mineral admixtures content of 10% FA and 10% MK can be applied to mass construction in practical engineering.